By Linda Sieg
TOKYO (Reuters) - Japanese Prime Minister Shinzo Abe has achieved much of his conservative security agenda since taking office in 2012 but unless he can revive his flagging popularity, his goal of revising the pacifist constitution is likely to elude his grasp.
Failure to achieve that goal by the 2020 target he announced three months ago would erode Abe's already weakened clout, dimming his chances of becoming Japan's longest-serving prime minister, lawmakers in his own Liberal Democratic Party said.
"Abe is filled with a desire to do this. He thinks revising the constitution is his greatest mission as a politician ... but can he really?," LDP lawmaker Katsuei Hirasawa told Reuters.
"To fail to achieve it would mean huge damage to Abe as a politician," said Hirasawa, who once privately tutored a youthful Abe. "It would be better if he'd never said it."
Abe's second term as LDP leader ends in September 2018 and his support has plunged to below 30 percent in some polls.
That is the lowest since Abe returned to power almost five years ago with a conservative agenda of reviving traditional values and loosening limits on the military that centered on amending the pacifist post-war constitution.
The decline has spurred talk that Abe may call a snap election before the year's end, even if that means risking the two-thirds super-majority needed to amend the constitution.
A general election does not need to be held until late 2018 but the main opposition Democratic Party is in disarray after its leader abruptly resigned and a novice local party led by popular Tokyo Governor Yuriko Koike has yet to become a national force.
"The goal would be to keep a majority and maintain the LDP government," veteran LDP lawmaker Takeshi Noda told Reuters, adding ruling party lawmakers were divided on the possible move.
Abe's proposal to clarify the military's ambiguous status by revising the constitution's war-renouncing Article 9 would be hugely symbolic in Japan.
Many conservatives see the U.S.-drafted charter as a humiliating imposition, while opponents to change view it as the basis of Japan's peace and democracy.
Any revision would spur concern in China, where memories of Japan's past military aggression persist.
Article 9 technically bans the maintenance of armed forces but has been interpreted by successive Japanese governments to allow the Self-Defense Forces, as the military is known, for exclusively defensive purposes. Historic changes enacted in 2015 expanded that to allow for limited collective self-defense, or aiding an ally under attack.
Backers of Abe's proposed revision say it would simply formalize those stances, although critics worry it would set the stage for further loosening restrictions, such as fighting in U.S.-led wars abroad.
Abe hopes to revive his flagging ratings with a cabinet reshuffle this week. A diplomatic coup or a security crisis, such as mounting tensions over North Korea's nuclear and missile program, could also help if voters see Abe as the safest pair of hands.
But a failure to stem the decline in ratings, which have fallen from highs of around 60 percent, would likely doom Abe's hopes of seeing the revision while he is still in office.
Formally amending the constitution is a politically tough task requiring approval by two-thirds of both houses of parliament and a majority of voters in a public referendum.
The ruling bloc now holds two-thirds majorities in both chambers, a rare situation that is unlikely to be repeated soon.
"Unless Abe regains the people's faith, revising the constitution will be impossible," Hirasawa said, noting the LDP's junior coalition partner, the Komeito, was now cautious about amending Article 9.
Earlier this year, Abe had been expected to comfortably win a third three-year term as LDP leader, setting him on track to become Japan's longest serving premier.
Suspected scandals involving cushy business deals for friends, a defense ministry cover-up that forced the resignation of his protege, Defence Minister Tomomi Inada, and voters' sense that Abe has grown arrogant have all contributed to the ratings drop.
Comments by former defense minister Shigeru Ishiba suggest he is positioning himself for a challenge to Abe's party leadership in 2018, although he has not formally declared his intention to run. Foreign Minister Fumio Kishida is widely seen in political circles as another potential candidate.
Media reports have said Abe may try to recruit Ishiba for his new cabinet line-up to forestall his challenge.
Abe has achieved several goals on the security front including creating a U.S.-style National Security Council, passing a state secrets act and 2015's reinterpretation of the constitution.
But formally revising the constitution is Abe's most cherished goal, in part because it eluded his beloved grandfather, Nobusuke Kishi, who quit as premier in 1960 due to a furor over a U.S.-Japan security pact.
Abe may cling to his the long-held goal in public but let it quietly drop in reality.
"He cannot achieve constitutional revision," said veteran political analyst Minoru Morita said. "It is an illusion."
(Additional reporting by Ami Miyazaki and Izumi Nakagawa; Editing by Lincoln Feast)